Parametric Study on Fast Reactors with Low Sodium Void Reactivity by the Use of Zirconium Hydride Layer in Internal Blanket

Abstract

A study on the sodium void reactivity reduction of 1,000MWe class fast reactors was performed. The target of this study is to materialize a core concept with a zirconium hydride layer in the internal blanket which satisfies the design criteria; that the possibility of the prompt critical by sodium voiding can be excluded at any time during reactor operation; and that the burnup reactivity is acceptably low, which is less than 2.5%dk/kk′. A series of parametric surveys were performed on the radial size of the internal blanket and the width of the zirconium hydride layer. The width of the layer was set to 3.0cm as the optimized specification which satisfies all the design criteria regardless of the fuel materials; oxide, nitride and metal.Transient behaviors of the cores were investigated during the unprotected loss of flow accident (LOF). The analyses showed that the oxide core was able to avoid sodium boiling. It was also observed that the cores with nitride and metal fuels had larger tolerance against the unprotected LOF: The outlet temperature were lower by 39 and 60°C compared with the oxide core.